1. Field of the invention
The present invention relates to a toner for electrophotography.
2. Description of the prior art
In general a toner for electrophotography is prepared as follows: a binder resin, a coloring agent and a desired additive are mixed and kneaded, and then the kneaded material is pulverized and classified.
A wax incompatible with the binder resin is generally added as one desired additive in order to prevent an off-set phenomenon at high temperature at the time of toner fixing by a heat-roller.
However, as the added wax is incompatible with the binder resin, it is difficult to disperse the wax in the form of small particles in the binder resin uniformly. Wax is liable to separate out from toner particles at the time of pulverization in toner-manufacturing process.
If a size of wax-particles separated out from toner particles is much smaller than a toner particle size, the wax-particles are removed in a classifying process. Even if the wax-particles are not removed, they adhere to toner particles, undergo the same processes as the toner particles and so do not influence adversely on a photosensitive member and copy images. If a size of wax-particles is almost the same as a toner particle size, wax-particles are not removed in a classifying process and they are incorporated into a final toner product.
As such separated wax-particles as incorporated into a final toner product do not contain a coloring agent and a charge controlling agent, they display chargeability completely different from that of the final toner product.
Wax-particles adhered to electrostatic latent images together with toner particles are not transferred onto copy paper even in a transferring process. They remain adhered to a photosensitive member.
These wax-particles remaining adhered to the photosensitive member are not cleaned by a cleaning blade in a cleaning process. The wax-particles fuse and stick to the photosensitive member. They are further spread thinly to form films on the photosensitive member, and to make matters worse, toner particles adhere to film-like wax to form lines of black spots on the photosensitive member.
As electrical charges do not leak from those films and black spots, fogs may be formed in copy images. When toner-particles are developed onto those films, the toner particles are transferred onto copy paper to cause image noises.
Recently, toner particle size is made small in order to elevate fineness of copy images. In the case of such small toner-particles, fine wax-particles need to be dispersed uniformly.